1. Field of the Invention:
This invention relates to fluid filtering apparatus, and, more particularly, apparatus for filtering or purifying liquids, such as oil, to remove moisture and particulate matter.
2. Description of the Prior Art:
The removal of impurities, including moisture and particulate matter from liquids, such as hydraulic fluids and lubricants, is a branch of technology which is increasing in importance as technology increases. One of the most important uses for fluid filters is in automobiles, in which the oil, used as a lubricant and as a coolant, must continually be filtered in order that the oil perform well and accomplish its designed functions. As indicated, there are two broad types of contaminants for liquids, including oil. These categories of contaminants are moisture or water, and particulate matter, which may be any type of foreign solid matter, such as sand, dirt, carbon particles, metal filings or chips, and the like. Typically, oil filters now used in automobiles include cotton layers, which are generally successful in stopping solid particulate matter, depending on the size of such particulate matter, and paper-type filters in which cellulose fibers, interwoven, are used to entrap and thus filter particulate matter from the oil. Neither of these types of filters is able to filter moisture, such as water, from oil. Other types of materials are required if such moisture is to be removed from oil.
There are generally two types of filters in use.
One is referred to as a full flow filter, in which the entire flow of fluid, such as oil, is subject to a filterint medium. The other type of filter is termed a bypass filter in which only a certain portion of the fluid flow is subject to filtration at any particular time. Over a total period of time, the entire flow of fluid, or the entire quantity or mass of liquid, is passed through or is subject to the filtering medium. Since only a portion of the fluid is passed through the filter at any time, there is not a requirement for a pressure relief valve, as is required with the full flow type filters. If the filtering medium becomes clogged, the result will merely be no filtration. However, there should always be sufficient fluid circulating so as to allow proper lubrication, if the fluid is a lubricating medium, or, in the case of hydraulic fluid, there should always be sufficient fluid to provide the appropriate hydraulic action.
With such bypass type filters, the filtering medium, or media, may be more effective than can generally be used in the full flow type filter. In the full flow type filter there is a possibility of a blockage of the fluid, or of a substantial decrease in the pressure of the fluid, if the filter becomes clogged. Accordingly, the filtering agent is generally limited in the size particles which can be filtered out and a pressure relief valve is generally provided. If the filter becomes clogged, then to continue the flow of fluid a pressure relief valve must be provided. Such pressure relief valve is generally a spring loaded valve set to open when the pressure or force against the spring reaches a pre-determined amount.
Some prior art filter apparatus have been developed which use heat in a chamber to remove water or water vapor by evaporation. The same heat may also at the same time remove, as from oil filters, fuel in the form of fuel vapor which has become trapped in the oil and which dilutes the oil. Fuel dilution in oil reduces the viscosity and accordingly the lubricating ability of the oil. A substantial disadvantage of such heat requirements is that a source of heat must be available. The source of heat in such filter apparatus is generally an electric heating element, powered from the alternator or generator of the engine.
With respect to particle size, typical filtering material, such as cotton fiber and/or felt, will generally filter particles down to about one micron, or perhaps slightly less. Paper filtering material may filter particles to about thirty or forty microns in size. However, the paper and the cotton and/or felt has no effect on water vapor, which passes right through the filter material with the fluid being filtered.
Some prior art filter apparatus, such as that described in the Burkness patent, U.S. Pat. No. 2,325,657, have combined filter media for filtering particulate matter, such as cotton, wool, steel wool, and the like, with some type of filtering medium for removing moisture, or odors and the like. The apparatus of Burkness includes two types of filter media, and it comprises a full flow type filter.
Another type of filter apparatus is disclosed in the Cook patent, U.S. Pat. No. 2,969,127. The Cook patent is designed to be used with an electrostatic precipitation unit by filtering large particles of dust and dirt from a flow of air. The filter is defined as an "expanded washable aluminum foil" filter, which comprises parallel rows or layers of rigid aluminum set substantially perpendicular to the flow of air, to provide a barrier against which larger particles of dust and dirt are trapped while allowing the air to pass therethrough. The aluminum is regular in configuration, and disposed in a fixed geometric and spaced apart relation with respect to the rows and layers. While the Cook apparatus is illustrated as comprising rigid twists of aluminum about a core, a very similar type filter exists in which a rigid honeycomb type filter is used rather than twists of aluminum about a central core. The layers of rigid honeycomb are bonded together and present again a large, rigid surface against which large particles of dust and air are trapped.
A bypass type filter is disclosed in the Kennedy patent, U.S. Pat. No. 2,843,268. This bypass type filter includes both a full flow cartridge and a part flow cartridge for filtering particulate matter from a liquid. In the full flow portion of the filter, and also in the part flow portion, a single filtering medium is used. A venturi is used in the part flow portion of the filter apparatus to help in providing a flow of fluid through the full flow portion of the apparatus.
The Kukowski et al patent, U.S. Pat. No. 2,936,891, is a typical illustration of a full flow type filter in which the fluid filtering medium is concentrically disposed within a cylinder. When the filter medium becomes substantially clogged, a pressure relief bypass opens to allow the flow of fluid through the filter apparatus, without any filtering taking place.
Only particulate matter is filtered by the Cook apparatus, the Kennedy apparatus, and the Kukowski apparatus. Obviously, the size of the particulate matter which the apparatus is able to filter varies, depending on the filtering media used, and the degree of saturation of the filtering media.
The filtering or purifying apparatus described and claimed herein includes material which will filter particles down to the size of about one micron or less and will also remove moisture or water vapor from the filtered material.